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    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>520</title>
</head>

<body>
    <canvas id="c"></canvas>
    <script>
        var body = document.body;
        var canvas = document.getElementsByTagName('canvas')[0];
        var a = canvas.getContext('2d');
        document.body.clientWidth;

        with (m = Math) C = cos, S = sin, P = pow, R = random;
        c.width = c.height = f = 600;
        h = -250;
        function start(a, b, c) {
            if (c > 60) {
                return [S(a * 7) * (13 + 5 / (.2 + P(b * 4, 4))) - S(b) * 50, b * f + 50, 625 + C(a * 7) * (13 + 5 / (.2 + P(b * 4, 4))) + b * 400, a * 1 - b / 2, a];
            }
            A = a * 2 - 1;
            B = b * 2 - 1;
            if (A * A + B * B < 1) {
                if (c > 37) {
                    n = (j = c & 1) ? 6 : 4;
                    o = .5 / (a + .01) + C(b * 125) * 3 - a * 300;
                    w = b * h;
                    return [o * C(n) + w * S(n) + j * 610 - 390, o * S(n) - w * C(n) + 550 - j * 350, 1180 + C(B + A) * 99 - j * 300, .4 - a * .1 + P(1 - B * B, -h * 6) * .15 - a * b * .4 + C(a + b) / 5 + P(C((o * (a + 1) + (B > 0 ? w : -w)) / 25), 30) * .1 * (1 - B * B), o / 1e3 + .7 - o * w * 3e-6]
                }
                if (c > 32) {
                    c = c * 1.16 - .15;
                    o = a * 45 - 20;
                    w = b * b * h;
                    z = o * S(c) + w * C(c) + 620;
                    return [o * C(c) - w * S(c), 28 + C(B * .5) * 99 - b * b * b * 60 - z / 2 - h, z, (b * b * .3 + P((1 - (A * A)), 7) * .15 + .3) * b, b * .7]
                }
                o = A * (2 - b) * (80 - c * 2);
                w = 99 - C(A) * 120 - C(b) * (-h - c * 4.9) + C(P(1 - b, 7)) * 50 + c * 2;
                z = o * S(c) + w * C(c) + 700;
                return [o * C(c) - w * S(c), B * 99 - C(P(b, 7)) * 50 - c / 3 - z / 1.35 + 450, z, (1 - b / 1.2) * .9 + a * .1, P((1 - b), 20) / 4 + .05]
            }
        }
        setInterval(() => { init() }, 0)
        function init() {
            for (i = 0; i < 1e4; i++) {
                if (s = start(R(), R(), i % 46 / .74)) {
                    z = s[2]; x = ~~(s[0] * f / z - h); y = ~~(s[1] * f / z - h);
                    if (!m[q = y * f + x] | m[q] > z) {
                        m[q] = z, a.fillStyle = "rgb(" + ~(s[3] * h) + "," + ~(s[4] * h) + "," + ~(s[3] * s[3] * -80) + ")", a.fillRect(x, y, 1, 1)
                    }
                }
            };
        }
    </script>

    <script>
    ({
        x: 10,
        foo: function () {
            function bar() {
                console.log(x);//undefined
                console.log(y);//30
                console.log(this.x);//20  
                console.log(this.y);//undefined
            }
            with (this) {
                var x = 20;
                var y = 30;
                bar.call(this);
            }
            
        }
    }).foo();
    
    // 假设块对象为a
    ({
        x: 10,//改为20
        foo: function () {
            // var x;
            // var y;//改为30
            function bar() {
                console.log(x);//如上，定义了x，但是没有值，undefined
                console.log(y);//如上 30
                console.log(this.x);//改变this指向a，输出a.x = 20  
                console.log(this.y);//a.y,不存在为 undefined
            }
            with (this) { //this就是a
                var x = 20; //更改a.x=20
                var y = 30; //a.y没有，本层查找y，赋值为30
                bar.call(this);//a对象
            }
        }
    }).foo();
    </script>
</body>

</html>